The proposed work will continue investigation of the properties of S-substituted isothiazolidinium salts formed when suitable aminothioethers (e.g., methionine) are oxidized by iodine and positive halogen reagents under conditions which disfavor hydrolysis to form sulfoxides. The project involves development of methods for synthesis of the title compounds, characterization of the chemical reactivity and other properties of the products, preliminary assessment of pharmacological properties, metabolism of various derivatives of methionine, and the possible existence and role of S-alkylisothiazolidinium salts in biological systems.